A flat-panel display element such as a liquid crystal display device is produced by a so-called photolithography technique in which a pattern formed on a mask is transferred onto a photosensitive substrate. An exposure apparatus used in the photolithography step includes a mask stage for supporting a mask, and a substrate stage for supporting a substrate. The exposure apparatus transfers the pattern of the mask onto the substrate through a projection optical system while sequentially moving the mask stage and the substrate stage. When the liquid crystal display device of the display elements is to be produced, a large glass substrate (plate) is used as the substrate. It is desired to increase a display region size. To respond to the desire, a so-called multi-lens scanning type exposure apparatus is mainly used. The multi-lens scanning type exposure apparatus is a scanning type exposure apparatus which continuously transfers patterns of a mask while scanning the mask stage and the substrate stage in synchronization with each other, and which has a plurality of projection optical units arranged as a projection optical system (see Japanese Patent Application Publication Laid-open No. H7-57986 for example).
The plurality of projection optical units are disposed on both sides in a scanning direction with an autofocus detection system interposed therebetween. A projection optical unit disposed forward in the scanning direction and a projection optical unit disposed rearward in the scanning direction are supported by a column (body of the exposure apparatus) through different support bodies. However, the column is slightly distorted and deformed in some cases when the mask stage or substrate stage is moved, and there is a problem that the optical property (imaging property) of the projection optical unit is varied and precise exposing processing can not be carried out. Especially in the case of a structure in which the plurality of projection optical unit are supported using different support bodies, relative positions of the plurality of projection optical units are varied and precise exposing processing can not be carried out. As a projection optical system of a scanning type exposure apparatus for producing a liquid crystal display device, an erect and equal-magnification system is generally used. Since the mask stage and substrate stage move in the same direction during the scanning and exposing operation, an unbalanced load with respect to the column becomes great and the above problem appears seriously. With the upsizing requirement of a substrate, the entire apparatus (entire column) is also increased in size, a sufficient rigidity of the column can not be secured, and the above problem appears more seriously. Hence, there is proposed an exposure apparatus in which a projection optical unit disposed forward in the scanning direction and a projection optical unit disposed rearward in the scanning direction are supported by a column through one surface plate (support body) (see Japanese Patent Application Publication Laid-open No. 2004-177468 for example)
In the exposure apparatus disclosed in Japanese Patent Application Publication Laid-open No. H2004-177468, a projection optical unit disposed forward in the scanning direction and a projection optical unit disposed rearward in the scanning direction are placed on a surface plate, and the surface plate is supported by a column through a spherical member possessed by a support section. The surface plate is provided with an opening for forming a projected image on a substrate, a torsional component is generated in the surface plate due to a friction force applied to the spherical member possessed by the support section and a weight of the projection optical unit itself, and there is a possibility that a deviation in a projection position (a deviation in the scanning direction, a deviation in a direction intersecting with the scanning direction, and a deviation in a rotation direction around an optical axial direction of the projection optical system) is generated between the projection optical unit disposed forward in the scanning direction and the projection optical unit disposed rearward in the scanning direction.
With the upsizing of the liquid crystal display element, the plate is also increased in size and at present, a plate (glass substrate) of one meter square is used, and a mask is also increased in size. If a pattern rule of a device desired for the exposure apparatus is constant, the same flatness as that of a small mask is required for a large mask. Hence, to suppress a warp or curl of the large mask to the same level as those of the small mask, it is necessary that the thickness of the large mask is made largely thicker than that of the small mask. Generally, a mask used for producing a TFT (Thin Film Transistor) type liquid crystal display (panel) is an expensive quartz glass, and if the size there of is increased, the producing costs are also increased. Further, costs for maintaining the flatness of the mask and costs caused by increase in inspection time of the mask pattern are also increased.
Hence, there is proposed a maskless exposure apparatus which exposes a pattern and transfers the same onto a substrate using a DMD (Digital Micro-mirror Device or Deformable Micro-mirror Device) or the like instead of a mask. In the maskless exposure apparatus, a surface plate on which a projection optical unit disposed forward in the scanning direction and a projection optical unit disposed rearward in the scanning direction are placed is supported by a column as in the conventional projection exposure apparatus using a mask, the maskless exposure apparatus has the same problem as that of the projection exposure apparatus which uses a mask.